Manzanos take up a hell of a lot of room. They grew wider a bushier than any other pepper I've ever grown. Also last summer was extremely hot which manzanos don't like as was evident by constant flower drop. The result was low yield. I heard similar results from other growers.
Pretty much this. The ones I grew last year were almost twice as wide as they were tall. I ended up having to put a bunch of stakes in the ground to tie the branches off. Very bushy plants. Love the purple flowers, though.
I have a Jiffy heated greenhouse, too. I use small plastic drinking cups and fill them with either coco coir or pro mix starting media. Pretty near 100% germination with everything I put in there. If you're using those peat pucks that come with it, just my opinion, but throw them away and start with a different medium.
My advice, and this is coming from someone's who has grown yellow manzanos all of one season:
Start them earlier than other peppers, seemed to take forever and a day to germinate and then get big and finally flower and fruit.
Shade is good for these guys.